Apparatus for combustion of fuels



Jan. 28, 1954 M. P. SWEENEY APPARATUS FOR COMBUSTION 0F FUELS 2 Sheets-Sheet 1 Filed April 30, 1958 LARGER souns 30 4/ 1o PROCESS men/0r Maxwefl Pafr/e/r Sweeney By Ms offomeys j {Au/1 M Jan. 28, 1964 M. P. SWEENEY APPARATUS FOR COMBUSTION OF FUELS 2 Sheets-Sheet 2 Filed April 3Q, 1958 United States Patent 3,119,379 APPARATUS FOR COREUSTION 0F FUELS Maxwell Patrick Sweeney, Philadelphia, Pa. Filed Apr. 30, 1958, Ser. No. 732,005 8 Claims. (Cl. 1224) This invention relates to apparatus for the controlled combustion of fuels, especially solid fuels of a refractory nature. In particular it relates to apparatus for the combustion of fuels in which the combustion temperature may be controlled to provide more eflicient operation and in which sol-id fuels of Various particle sizes may be burned.

Consumer demand and increased industrial capacity have, in recent years, progressed beyond normal expectations. Paralleling and even surpassing these demands is the demand for increased power. This invention concerns itself with one of the sources of this power, the combustion of fossil fuels, and with apparatus for obtaining heat energy from such fuels.

In modern practice heretofore, much heat energy has been generated by the combustion of pulverized solid fuel in boilers. The solid fuel is crushed and finely ground to the extent that 60-85% {by weight will pass a 200 mesh screen and all will completely pass through a 100 mesh screen. It is mixed with air and blown into a combustion boiler enclosure Where it receives, by radiation and convection, suflicient heat from the surroundings to initiate combustion, thereby forming a flame.

Several important diflieulties have been experienced in the combustion of pulverized fuels as it is now carried out.

In the first place it is necessary to pulverize the solid fuel very thoroughly before it is burned. Thus in conventional apparatus in order to ignite and form a stable flame, suflicient heat must be transferred to the particles within about 0.02 second to cause them to-ignite spontaneously. Again combustion of each solid particle must be substantially complete within about 0.05 second. The very small size of the coal particles needed to meet these requirements, raises problems. For example, the fly ash obtained is diflicult if not impossible to remove from the flue gases, causing smoke and polluted atmospheres. This problem is aggravated when it is attempted to burn refractory fuels such as petroleum coke, coke breeze and anthracite. Suoh fuels are even more difiicult to ignite and so must be ground even finer than, say bituminous coal. Since almost invariably these refractory fuels are also more difficult to grind evenly to a given fineness, power and equipment requirements are often as much as live times as great as for bituminous coal, and become a very substantial part of the cost in power generation.

Another disadvantage experienced with conventional boiler designs is that the flame is too hot, normally in the region of 30003500 F. This causes fusion and decomposition of the ash particles. The fused ash tends to flux refractory linings in the furnace and form an enamel-like deposit on the boiler tubes. Both of these effects result in an increase in maintenance cost.

Still a further disadvantage inherent in conventional boiler designs is that the efficiency of the radiant portion of the unit tends to decrease with increase in throughput. In order to obtain large amounts of low cost power, boiler sizes have progressively increased in size. As fuel throughput increases, the flame size also increases necessarily. This flame normally consists of a hot center zone and successively cooler concentric outer zones. As the flame size is increased, the concentric cooler zones become of greater thickness and as such, act as an insulating sheath. This has the effect of reducing the transfer of heat per unit of fuel throughput to the tube-containing ice 2, walls of the flame section of the boiler enclosure, while, at the same time, reflecting the radiant heat back into the hot center zone of the flame, thereby creating still higher temperatures in this zone with the undesirable eifect already described.

Attempts have been made to overcome the diifieulties just described lby replacing the one large flame with a number of smaller flames, and locating these nearer to the walls of the flame section of the boiler enclosure. However, locating the flame near heat absorbing walls of the flame section has not been entirely successful because impingement of a flame containing corrosive molten and volatilized ash icomponents causes rapid corrosion of tubes and refractory. A number of smaller flames does effectively reduce the depth of the cooler zones of the flame through which heat radiation \must take place. Transfer of heat to the walls of the flame section of the boiler enclosure is thereby more efliciently accomplished and the temperature in the center zone of the flame is likewise at a somewhat lower level. However, flame temperatures having been reduced in this manner, ignition problems arise and flame blowouts may frequently be encountered, particularly withrefractory fuels, so that at best, a compromise as to flame size must be resorted to, thus causing ash melting and volatilization with attendant fouling and corrosion, and sacrificing eflicient utilization of heat transfer surface for the sake of smooth operation.

Other forms of combustion device than the conventional boiler have been developed for finely divided solid fuels, normally in conjunction with chemical processes requiring a constant supply of highly heated solids. Thus, for example, it has been proposed to establish a dense 1 turbulent fluidized bed of finely divided solid fuel, and blow an oxygen containing gas through the bed. A part of the solid fuel is thereby oxidized, heating up the remainder. While the technique is satisfactory for certain applications, it, too, has drawbacks.

Where finely divided solids are maintained in a fluidlike, turbulent, dense phase suspension by a stream of fluidized gas flowing upward at a sufficiently high rate to be economical, a substantial portion of the gas invariably rises through the bed of solids in the form of bubbles, so that contact between the solids and the gas is imperfect. If aeration or fluidization is the sole function of this gas stream, little difficulty is presented but where the gas is used to burn a part of the solids, the formation of bubbles presents a real problem.

Passage of the combustion air through the solids bed in the form of bubbles reduces the amount of contact between the air and the solids so that much of the air emerges from the solids bed unreacted. Furthermore, a deficiency of air near most of the solid particles in the bed results in the formation of large amounts of CO. As this CO emerges from thebed, it mixes with the unreacted air and creates an eflect known as afterburning in which some of the CO is burned to produce an overheated zone above the bed. Unless the walls surrounding this zone are lined with refractory materials, and the cyclone separators for removal of entrained solids are resistant to very high temperatures, much damage can result. Even so, this overheating effectively shortens the life of the construction materials. Any CO formed in the bed that is not burned in substantial contact with solid particles to be heated, represents a loss in potential heating value.

To prevent these occurrences, it has been proposed to hold a very large amount of solids in the fluidized bed, thereby presenting more carbon surface area, for an ex tended period of time, to obtain more complete combustion. This requires a large combustion vessel. Where The density of a socalled fluidized bed ranges from say 60 'to of the loose packed bulk density of the solids the fuel being burned is refractory, i.e., difficult to burn, an even greater amount of solids is required to be present in the bed, if the oxygen in the air is to be completely reacted. This is particularly so in cases Where it is desired to keep the combustion temperature relatively low, as in cases where the solids are to be used in a subsequent cracking or pyrolysis process. Added together, these factors cause the combustion vessel to become enormous and costly.

It has also been proposed from time to time to conduct combustion of solids in a disperse phase in a transport conduit for the purpose of reheating solid particles. These particles are then separated from the gas by passing the mixture through a high temperature cyclone separator. To date this technique has not been used in connection with furnishing heat to heat transfer surfaces as in boilers. Moreover the systems in which it has been used have had the disadvantage that cyclone separators for the high temperature conditions encountered are very expensive and bulky, the losses of solids from them are relatively large; and no control over particle sizes is obtained.

It is an object of the present invention to provide apparatus for the combustion of fuels which is more efficient than has been available hitherto.

It is another object of the invention to provide apparatus for the combustion of fuels in which flame tern peratures may be controlled and varied below about 2500 F.

It is another object of the invention to provide apparatus for the combustion of fuels in which melting, degradation and volatilization of harmful ash components is minimized.

It is another object of the invention to provide apparatus for the combustion of fuels in which fouling and corrosion of boiler tubes and formation of slag thereon is eliminated.

It is another object of the invention to provide apparatus for the combustion of fuels in which handling of high temperature flue gases in conduits and cyclones is avoided.

It is another object of the invention to provide apparatus for the combustion of fuels in which CO formation and afterburning are minimized.

It is another object of the invention to provide apparatus for the combustion of fuels in which combustion air requirements are reduced.

It is another object of the invention to provide ap paratus for the combustion of fuels in which the size of the furnace enclosure may be reduced.

It is another object of the invention to provide apparatus for the generation of steam in which heat absorption by boiler tubes is improved.

It is another object of the invention to provide apparatus especially adapted for the combustion of refractory fuels, diflicult to burn in conventional apparatus.

It is another object of the invention to provide apparatus for the combustion of solid fuels in which grinding of fuel is substantially reduced.

It is another object of the invention to provide apparatus for the production of heated, finely divided solids in which solids within a narrow particle range can be obtained.

It is another object of the invention to provide apparatus for the production of heated, finely divided solids in which the solids may be heated by combustion at a temperature other than that at which the solids are to be utilized.

It is another object of the invention to provide apparatus for the combustion of fuel and the production of heated solids and steam in which any desired fraction of The density of a dilute or disperse phase mass is less thlag about of the loose packed bulk den ity of the so 1 s.

the heat produced may be used either in the heating of solids or the production of steam.

It is another object of the invention to provide apparatus for the combustion of fuel in which the temperature of the exit gases and the quantity of solids entrained therein is minimized.

In accordance with the invention these and other objects are attained by means of a combustion apparatus characterized in that the combustion is carried out in a disperse phase mass of hot solids and oxygen containing gases in which the weight ratio of solids to oxygen is at least 25:1 and that hot gases and solids from said mass are brought into heat transfer relationship with a heat transfer surface.

Preferably the fuel is introduced into a vertically upwardly moving mass of gases and entrained solids, and burned in that mass. The heat of combustion raises the temperature of the solids rather than of the products of combustion so that, considering the large quantity of excess solids present, the maximum temperature of the products of combustion may be kept below the fusion temperature of the ash.

More specifically, in a preferred form of the invention fuel is injected semi-tangentially into a disperse-phase upwardly moving stream of gases and entrained solids.

By semi-tangentially it is meant that a substantial amount of the solids is introduced toward the center of the vortex, rather than along its outer edge. Defined more rigorously, it may be said that when solids are introduced semi-tangentially through an inlet duct into a vessel having a substantially circular cross section, the axis of the inlet duct lies in a plane tangent to a cylinder concentric with the axis of the vessel and having a radius not greater than the radius of the vessel. Preferably the radius of the cylinder is not less than /2 the width of the inlet duct.

The resultant of the upwardly moving stream and the semi-tangential feed is a vortically upwardly moving mass. The vortical motion of the mass hurls the heavier solid particles to the periphery whence they fall downwardly and are again entrained in the upwardly flowing stream. A preselected fraction of the solids having an intermediate size range may be removed at a point on the mass above the point of feed introduction. The mass gradually loses its vortical motion and passes into an enlarged heat transfer zone. The reduced velocity of the gas stream causes the solids to fall in a fountain or umbrella-like pattern. A heat transfer surface is arranged adjacent the falling solids and heat is given up by the solids through contact with and radiation and convection to the heat transfer surface. Heat is also conveyed to the heat transfer surface by contact with hot gases.

As the solids fall they are collected in a mass at the bottom of the heat transfer zone. This mass is preferably maintained in an aerated or fluidized condition. Solids may be withdrawn from the fluidized mass and recycled to the combustion zone, or to an exterior system where hot solids are required.

After at least a portion of the fine solids have gravitated out of entrainment with the gases, the gases may be passed into contact with a further heat transfer surface for the recovery of additional heat.

The invention may be used with any type of fuel, ranging from gaseous fuels such as methane or propane to liquids such as Bunker C fuel oil or other residual oils, to solids such as coal, lignite or coke. It is particularly useful, however, with refractory solid fuels, because the necessity for intimate grinding and very high flame temperatures encountered in conventional burners is eliminated.

The solids which are employed in the invention may vary widely in character. They may be the solid fuel itself, introduced in excess, or a residue or fraction thereof recycled to the vortical bed after having been removed 'rnoved by burning. for conducting such burning operation because the tem- .per circular header 17 to a lower circular header 18. .line 7 is provided for supplying a working fluid to die therefrom. Alternatively they may be an inert material such as sand or alumina. Inert materials are particularly useful when the fuel to be burned is a gas or a liquid.

In some instances, the solids may be partly fuel and partly inert. For example, many processes such as the cnacking of petroleum, are carried out in the presence of finely divided solids, either catalytic or non-catalytic. During the process the solids become contaminated with a layer of carbonaceous material, which is normally re- Tlhe present process is well suited perature may be kept below the level where cracking or spalling of the solids would occur and because it is possible to simultaneously heat and classify the solids, eliminating material which is too fine as well as particles which have grown too large by successive depositions of carbonaceous material.

In this connection it may be pointed out that in one aspect the invention includes a method for classifying finely divided solids which comprises introducing a stream of gases and entrained finely divided solids having a wide range of particle sizes into a vortically upwardly moving -mass of gases and entrained solids, separating large particles downwardly from said mass, carrying fine particles 'of a combustion device according to the invention.

FIG. 2 is a view in horizontal section along the line 2-2 of FIG. 1.

FIG. 3 is a fragmentary view in vertical elevation showing a semi-tangential inlet in an apparatus of the type shown in FIG. 1.

FIG. 4 is a view in horizontal section along the line 4-4 of FIG. 1.

FIG. 5 is a view in horizontal section along the line 55 of FIG. =1.

FIG. 6 is a fragmentary view in perspective showing details of the interior of the apparatus of FIGS. 1-5.

Referring to FIG. 1, a combustion device according to the invention comprises a heat exchange vessel it) and a combustion tube 11. The combustion tube is located beneath the heat exchange vessel and has an extension 12 reaching through the bottom of the heat exchange vessel and up into the lower portion of the vessel. Inside the vessel it) are located two sets of heating tubes 13 and 14. The first set 13 extends from a drum 15 downwardly to a circular header 16. A line 9 supply a working fluid, e. g., water, to the header 16. A line 8 removes vapor, e.g., steam, from the drum 15. As shown more clearly in FIG. 4, the tubes of the set 13 are joined by webs such 13a to form a continuous dome-like surface in the interior of the heat exchange vessel it The second set of beating tubes. 14 extends trom an upheader 18. A line 6 is provided for withdrawing vapor from the header 17.

The combustion tube 11 is provided at its lower extremity with an inlet duct 19 by means of which a stream of gas may be directed upwardly through the tube. Directly abovethe entrance of the duct 19 into the tube 11 is located a grid 26 for preventing solid particles from falling down into the duct 19. At a point above the grid 29 is located acircular deflector 21 which serves to guide solid particles fflling down along the walls of the tube 11 into the center of the tube. At some distance above the I deflector 21 is located a semi-tangential feed inlet 22. in accordance with the definition given above, the axis aa duct 19 at the bottom of the combustion tube 11.

6 Above the semi-tangential inlet 22 is located a solids inlet 23 which again is positioned semi-tangentially to the tube 11. An auxiliary duel inlet 24 is positioned between the inlet 2.2 am the deflector 21' and an auxiliary air inlet 25 is positioned between the inlet 22 and the inlet 23.

A duct 26 extends from the bottom of heating vessel It) and connects with the solids inlet 2-3 whereby solids gathering in the bottom of the heat exchange vessel can be circulated to the combustion tube 11. Carrying gas for this purpose may be injected into line 23 through line 23a. The duct 26 has an extension 27 through which excess solids may be withdrawn as product, it desired.

As will appear more clearly below, the invention in its process aspects envisions that a bed of fluidized solids will be collected in the bottom of the heating vessel 10'. To maintain such solids in fluidized condition a series of radial aeration ducts'suoh as 28 and 29 are arranged around the bottom of the heating vessel. The aeration ducts have extensions 3-0 distributed along their lengths enabling an innocuous gas such as steam to be delivered at a number of points across the bottom of the heating vessel It) to maintain the bed in the bottom of the vessel in fluidized condition.

At the top of the combustion tube 11 is located a hollow deflector ring 31. The deflector ring is mounted on the combustion tube by means of struts 32 and has a horizontally extending plate 33 which reaches for a considerable distance beyond the combustion tube extension 12. The plate 33 on its lower surface has two circular downwardly extending rings 34 and 35. A circular baflle plate 35 is mounted on the floor of the heating vessel 10 coaxially with the combustion tube 11. It has a greater radius than the combustion tube and extends upwardly to fit between the two rings 34 and 35. As will appear more clearly, the purpose of this battle is to segregate solids passing between the upper edge of the combustion tube 111 and the deflector ring 31 from solids falling down from the upper :portion of the heat exchange vessel 10'.

In operation, fuel is fed to the combustion tube 11 through feed inlet 22. This fuel maybe solid, liquid or gaseous. If it is a solid or a heavy liquid it is entrained in agas which may be entirely inert,e.g., steam or nitrogen, or which may contain a certain quantity of tree oxygen. In any case, thefuel is made gasiform by entraining it in a disperse phase in a carrier gas. Of course, if the fuel is a gas to begin with no carrier is needed. This also proves true where the gas is a light liquid which can be completely vaporized.

An oxygen containing-gas is introduced through inlet This gas may be pure oxygen, a mixture of oxygen and an inert gas, e.g., air, or oxygen plus an auxiliary fuel, the oxygen being present in excess over the auxiliary fuel. The mixture of gases introduced through duct 19 flow upwardly through the combustion tube 11 at 13. velocity on the order of 10-80 ft./ sec. The mixture of fuel and carrier gas introduced through the duct 22 enters combustion tube 11 semi-tangentially at a velocity which may vary con- 'siderably but which will in general be between about 10 and about ft./ sec. The resultant of the two streams, i.e., the stream introduced. semi-tangentially through the duct 22 and the stream moving upwardly through the combustion tube L1 is an upwardly vertically moving mass of gases and disperse phase solids. It is characteristic of the invention that the total amount of oxygen introduced into this mass is considerably less than the total amount of solids. More specifically the solids introduced are always at least 2 /2 times as great by weight as the total the coal. In practice the density of the stream will normally amount to about 0.1-0.5 lb./cu. ft. It will enter the combustion tube 11 at a velocity of 10-100 ft./sec. It meets the stream of oxygen containing gas moving at right angles to its direction upwardly through the tube 11. An upwardly vertically moving mass is thus formed and at the same time the coal begins to burn. Before it has undergone sufficient combustion to raise its temperature much above say 2500" F., a stream of relatively cool solids in troduced through solids inlet 23 joins the vertically moving mass. The amount of solids which are recirculated through line 23 is such that the ratio of solids to oxygen containing gas is not below 2.5:1. As the solids move upwardly in the vertically moving mass, the larger particles, say above 500 microns, are thrown to the periphery of the mass and being heavier, slide down along the walls of the tube 11. When they reach the deflector 21 they are tossed out into the center of the tube 11 and are caught up in the upwardly flowing stream of oxygencontaining gases introduced through duct 19. A-fter this cycle has been repeated a few times the solids will have become smaller and will move upwardly with the vertioally moving mass. Thus, the present apparatus has a built-in control of particle size and it is not necessary to conduct a rigorous grinding operation on the fuel before it is introduced.

As the vertically moving mass reaches the top of the tube 11, particles of intermediate size, say 500 microns to 40 microns, are on the periphery of the mass. They fiow outwardly through the annular space 37 between the upper edge of the tube 11 and the deflector ring 31. They are then shunted downwardly by plate 33 and ring 35 into the annular compartment 33 between the combustion tube extension 12 and baflle plate 36. This provides a reservoir of hot particles of controlled size which may be used as a Source of such particles for various process applications. These particles are kept in fluidized condition by means of an aenation gas introduced through the radial lines such as 28 and 29 and their extensions 30. Solids from the compartment 38 may be Withdrawn through line 41.

The central portion of the stream containing the smallest size particles, say less than 40 microns, moves upwardly through the combustion ring 11 and passes through the center of the deflector ring 31. At this point it has lost much of its vertical motion and passes generally linearly upwardly into the interior of the first set of heating tubes 13. As the gases and entrained fine solids move intothe enlarged space, the velocity of the gases diminishes and a fountain-like effect occurs with the solids moving upwardly and then falling downwardly along the heating tube set 13. The heat of the solids is thus delivered to the tubes by conduction, radiation, and convection. The solids are cooled and fall downwardly into the bottom of the heating vessel 10. There they form a bed 39 which is maintained in a fluidized state by means of a fluidizing gas, e.=g., steam, introduced through the radial lines such as 28 and 29 and their extensions 30.

The gases emerging from the combustion tube 11 cannot pass through the tubes of tube set 13 because, as desoribed above, the heating tubes are joined by webs 13a to form a continuous surface. Instead, when the solids drop out of the gases into the bottom of the heating vessel 10, the gases pass upwardly between the first set of heating tubes 13' and the second set of heating tubes 14. They thus serve to heat the second set of heating tubes and are themselves cooled. After giving up their heat to the second set of heating tubes 1 the gases are removed from the apparatus through the exit duct 40.

Working fluid such as water is furnished to tube set 13 through line 9 and set 14 through line 7. Steam is removed through lines 8 and 6 respectively.

As described above, the device is used to generate hot solids as well as furnish steam.

If it is desired to use the invention only to generate steam, the deflector'ring 31, plate 33 and battle 36 may be eliminated entirely, so that the solids collected in the bottom of the heat exchange vessel 10 are not segregated as to size. The vertical component of the mass moving up through tube 11 is reduced to the minimum required to hurl oversizcd solids to the walls of the tube, so that a maximum proportion of hot solids is delivered into the heat exchange vessel to give up their heat to the tube set 13.

If on the other hand, it is desired to increase the proportion of solids collected in compartment 38 this may be done by giving a greater vertical velocity to the vertically moving mass so that more solids will be thrown toward the periphery of the mass and removed through the space 37. One means for increasing the rotational velocity of the vertical moving mass is to inject additional gas at high velocity through the line 25. This gas may or may not contain free oxygen.

Again, if it is desired to increase the temperature of the solids in bed 39, and in the compartment 33, the fluidizing medium furnished through the radial aeration lines such as 28 and 29 may comprise oxygen and a gaseous fuel, such as methane, which will burn in the bed 39 and in the compartment 38. Where the solids collected are combustible the same effect may be obtained by omitting the gaseous fuel and furnishing oxygen, or an oxygen containing gas, relying upon combustion of a portion of the solids :to furnish desired heat.

Obviously if it is desired to heat only the solids in compartment 38, or only the solids in bed 39, oxygen or oxygen and fuel may be delivered to the appropriate section independently. For simplicity, means to effect this have not been shown in the drawing.

Again it may not be desirable to recirculate solids from the bed 39 back to the combustion tube 11. In this case the line 23 may be closed off, solids may be removed through the extension 27 and fresh solids furnished to the combustion tube 11 through the line 24.

It will be readily understood 'by those skilled in the art that other modifications of the details shown may be used without departing from the invention. For example, the solids instead of being introduced through lines 22 and 23 could be introduced at the bottom of the tube 11, for example, in line 19, along with a portion of the air. Also, while entrances 22 and 23, for fresh feed and recirculated solids, respectively, are shown as separate entrances for purposes of clarity, it may be preferred to mix them together prior to their introduction into the tube 11, thereby achieving a uniform mixture and preheating the fuel almost instantaneously to its ignition point.

The invention will be further described by means of the following specific example, which it will be understood, is given for purposes of illustration only.

An apparatus of the type shown in the drawings is constructed, the tube 11 being 40 ft. long and 10 ft. in diameter. 45,000 lbs/hr. of coal reduced to less than A" in size is entrained in 200 cubic ft./sec of air in line 22 and delivered to the tube 11. 1500 cubic f-t./sec. of air is furnished through line 19. 400 lbs./ sec. of recirculated solids and 22,000 lbs./ hr. of process solids from line 23a are introduced through line 23, entrained in 300 cubic ft/see. of air. The total ratio of solids to oxygen introduced into tube 11 is thus about 12.321. 50,000 lbs/hr. of steam at 1000" F. and 1200 p.s.i.g. is withdrawn through line 6 and 500,000 lbs/hr. at 570 F. and 1225 p.s.i.g. is withdrawn through line 8. 20,000 lbs/hr. of heated solids having a particle size above about 0.002 inch are withdrawn through line 41 and 2000 lbs/hr. of solids having a particle size below about 0.004 inch are withdrawn through line 27.

It is obvious that many other variations and modifications will occur to those skilled in the art and the invention is not intended to be limited to the specific embodiments which have been described above.

What I claim is:

1. Combustion apparatus comprising a shell, heat exchange means positioned in said shell, a combustion tube beneath said shell and extending upwardly into said shell, means for introducing solids semi-tangentially into said tube at a point beneath said shell, means for blowing solids upwardly through said tube into said shell, means for maintaining a fluidized solids bed in the bottom of said shell for receiving solids blown upwardly through said tube into said shell.

2. The apparatus claimed in claim 1 and comprising means for conveying solids from said bed to said combustion tube.

3. Combustion apparatus comprising a shell, heat exchange means in said shell, a combustion tube positioned beneath said shell and extending upwardly into said shell, means for introducing solids into said tube, at a point beneath said shell, means for blowing solids upwardly through said tube into said shell, a collar in said shell about said tube, said collar, with said tube, defining an annular chamber in the bottom of said shell, and a baffie ring at the top of said tube adapted to deflect solids moving up said tube along the walls of said tube into said annular chamber and to permit gases and solids moving up the center of said tube to contact said heat exchange surfaces in said shell.

4. The apparatus claimed in claim 3 wherein said heat exchange means comprises an outer set of heat exchange tubes and an inner set of heat exchange tubes, said inner set being positioned above said combustion tube to receive gases and solids emerging from the center of said tube.

5. The apparatus claimed in claim 3 and comprising 3 10 means for maintaining fluidized solids in the bottom of said shell.

6. The apparatus claimed in claim 5 and comprising means to convey solids from said bed to said combustion tube.

7. Combustion apparatus comprising a heat exchange chamber, an outer set of heat exchange tubes located in said chamber adjacent the walls thereof, a dome-like inner set of heat exchange tubes located in said chamber inside said outer set, a combustion tube positioned beneath said chamber, extending upwardly into said chamber and arranged to discharge inside said dome-like inner set of heat exchange tubes, means for introducing solids into said tube at a point beneath said chamber, means for blowing solids upwardly through said tube into said chamber and means for maintaining a fluidized solids bed in the bottom of said chamber for receiving solids blown upwardly through said tube into said chamber.

8. The apparatus claimed in claim 7 and comprising means for conveying solids from said bed to said combustion tube.

References Cited in the file of this patent UNITED STATES PATENTS 973,468 Bettington Oct. 25, 1910 1,724,041 Plaisted Aug. 13, 1929 1,812,080 Chapman June 30, 1931 1,852,968 Hillhouse Apr. 5, 1932 1,969,501 Chapman Aug. 7, 1934 2,494,465 Watson et al. Jan. 10, 1950 2,518,800 Lester Aug. 15, 1950 2,666,632 Culver et al. Jan. 19, 1954 2,788,311 Howard et al. Apr. 9, 1957 FOREIGN PATENTS 349,915 Great Britain June 1. 1931 

1. COMBUSTION APPARATUS COMPRISING A SHELL, HEAT EXCHANGE MEANS POSITIONED IN SAID SHELL, A COMBUSTION TUBE BENEATH SAID SHELL AND EXTENDING UPWARDLY INTO SAID SHELL, MEANS FOR INTRODUCING SOLIDS SEMI-TANGENTIALLY INTO SAID TUBE AT A POINT BENEATH SAID SHELL, MEANS FOR BLOWING SOLIDS UPWARDLY THROUGH SAID TUBE INTO SAID SHELL, MEANS FOR MAINTAINING A FLUIDIZED SOLIDS BED IN THE BOTTOM OF SAID SHELL FOR RECEIVING SOLIDS BLOWN UPWARDLY THROUGH SAID TUBE INTO SAID SHELL. 